1. Field of the Invention
The present invention relates to an apparatus for controlling the moving position of an object and, more particularly, to an apparatus suited for control of the moving position of an optical system of a camera.
2. Related Background Art
In a lens-shutter type camera, if the focal length changes, the f-number and the lens extension amount upon focusing normally change accordingly. Therefore, focal length detection means is required to achieve f-number correction and lens extension amount correction.
As the most popular one of such focal length detection means, means for moving a brush on a code pattern of gray codes in synchronism with movement of the focal length is known. In addition, a method of detecting the focal length using a variable resistor whose output changes in synchronism with movement of the focal length is known. In terms of detection with high accuracy, this method is more effective than the above-mentioned means.
In the conventional focal length detection means using the variable resistor which can detect the focal length of a zoom lens with high precision, since the focal length is detected using an A/D converter during zooming, an accuracy error of the A/D converter occurs and focal length detection accuracy is impaired due to the influences of, e.g., a voltage drop upon energization to a zoom motor, noise of the motor, and the like. In addition, when one A/D conversion period is long, a stop error inevitably occurs due to a shift in detection time in correspondence with the period. As a result, the lens cannot be accurately stopped at a target zooming stop position the TELE (telephoto side) end upon driving in the TELE direction or the WIDE (wide-angle side) end upon driving in the WIDE direction!.
Furthermore, with the conventional means, since the linearity of the A/D converter suffers upon a voltage drop of a power supply voltage, if focal length detection is performed during charging of a stroboscope device, the detection cannot be normally performed.